The operation of airlines and airports today focuses on achieving maximum efficiency to keep operating costs as low as possible while continuing to provide travelers with a safe and economical mode of travel. Moving aircraft effectively on the ground between landing and takeoff improves airport operating efficiency. The increased aircraft ground traffic found at many airports, however, may be accompanied by an increased risk of ground incidents involving aircraft, ground vehicles, and even passengers and ground personnel. Improving the efficiency of airport ground traffic should not be at the expense of increased ground safety risks. Effective airport surface traffic management is a critical aspect of maintaining efficient aircraft ground movement in the congested runways, taxiways, and ramps in today's airports. Air traffic control and ground control personnel try to keep ground traffic moving so aircraft can take off on time and delays are minimized.
Runway and ramp congestion caused by increasing numbers of flights, stringent aircraft scheduling requirements, and efforts to squeeze large jets into gates originally designed for much smaller aircraft all contribute to airport traffic jams and reduced maneuvering space in the ramp area. Some studies have indicated that the location of most of the incidents resulting in damage that occur during aircraft ground travel happen at the ramp entry or exit area. At this location, taxi lines leading into and out of the gate area converge, and an aircraft is less likely to be in communication with ground traffic or other controllers. Increased pilot and cockpit crew situational awareness is required in these situations.
Once an aircraft has landed, a pilot currently must use the aircraft engines to power the aircraft from the landing runway to its ultimate parking location at a gate or elsewhere. During taxi, the ground movement of the aircraft must be carefully controlled, and the pilot is required to maintain positive control of the aircraft's direction and speed of movement. In addition, the pilot must be alert and able to check visually the location and movements of everything else along the aircraft's taxi path. An awareness of other aircraft that are taking off, landing, or taxiing and consideration of the right of way of others is essential to safe aircraft ground movement in today's congested airports. To be able to maintain the high level of situational awareness required for safe taxiing, a pilot must be able to keep his or her eyes on the aircraft's exterior environment rather than in the cockpit. This is difficult to do when a pilot must focus not only on careful operation of the aircraft engines during taxi, but also on the aircraft travel speed as the pilot tries to achieve a required time of arrival at a specified traffic flow point at a busy airport. These challenges are additionally present during taxi-out.
The development of airport surface traffic management systems for ground traffic control is designed to provide optimized taxi clearances that eliminate runway delays, especially runway crossing delays, to enable more efficient use of runways. Pilots using such a system must comply with speed- or time-based requirements to efficiently navigate a taxi route so that the movement of all surface traffic can be coordinated precisely. One study of pilots using a simulation of this type of airport surface traffic management system during taxi-out departure from the ramp area to the runway indicated that pilots had more difficulty maintaining a commanded speed for a long distance and spent a significant amount of time with heads down looking at a speed display. (Bakowski et al, Proceedings of the Sixteenth International Symposium on Aviation Psychology, 44-49, Dayton, Ohio, Wright University, 2009) The pilots participating in the study indicated that staying within the commanded speed was not a reasonable requirement and negatively impacted safety by interfering with primary taxi tasks to navigate the aircraft and maintain visual separation from other aircraft and obstacles.
While most airports have recommended taxi speeds during aircraft ground travel after landing and prior to takeoff, it is difficult to set a firm rule that defines a safe taxi speed. What is safe under some conditions may be hazardous under others. A primary requirement for safe taxiing is maintaining safe positive control, which includes the ability to stop or turn where and when desired. Too great a taxi speed must be avoided, since high ground speeds can exert excessive strains on an aircraft and result in a lack of control on turns. Taxi speeds generally may vary from about 10 knots (11.5 miles per hour) to about 20 knots (23 miles per hour), with the lower speed recommended for turns and the higher speed recommended for straight sections of the runway or taxiway. More aggressive operators, typically not in hub airports, may vary taxi speeds from about 15 knots to about 25 knots (17.3 to 28.8 miles per hour).
Systems for controlling aircraft speed during flight have long been available. One such system is described in U.S. Pat. No. 4,490,793 to Miller. These systems operate to control speed by supplying appropriate commands to engine automatic throttle controls to maintain a target speed. Pilots typically control aircraft ground travel speed in much the same way, by varying throttle inputs to the engine to adjust engine operation, thereby regulating the speed of travel of the aircraft on the ground. The use of an aircraft's main engines to move an aircraft on the ground presents challenges, however, ranging from the dangers associated with jet blast and engine ingestion to the reduction in useful engine life caused by ingestion of foreign object debris and continuous engine operation at low taxi speeds rather than optimal air speeds. In addition, aircraft ground travel using the aircraft engines consumes significant amounts of fuel and increases fuel costs.
U.S. Pat. No. 7,469,858 to Edelson, owned in common with the present invention, describes a geared wheel motor design that may be used to move an aircraft during ground travel and taxiing without relying on the aircraft's engines or external tow vehicles. Moving an aircraft on the ground during taxi by means other than the aircraft's main engines or turbines has also been described elsewhere in the art. U.S. Patent Publication No. US2009/0294577 to Rogues et al, for example, describes a device that enables an aircraft to move autonomously on the ground that employs a very specifically defined spiral drive gear to turn an aircraft wheel. It is suggested that the speed of this device can be controlled, but it is not suggested how speed could be controlled or that the direction of travel could be automatically controlled. In U.S. Pat. No. 7,445,178, McCoskey et al describes a powered nose aircraft wheel system useful in a method of taxiing an aircraft that can minimize the assistance needed from tugs and the aircraft engines. A precision guidance system including ground elements that interact with aircraft elements is disclosed for controlling direction of movement of the aircraft on the ground during taxi. McCoskey et al, however, is silent with respect to whether or how the speed or direction of aircraft ground travel could be automatically set, controlled, or maintained. U.S. Pat. No. 7,226,018 to Sullivan also describes a wheel motor useful in an aircraft landing gear wheel designed to provide motive force to an aircraft wheel when electric power is applied. Sullivan also fails to suggest whether or how the speed or direction of aircraft ground travel could be set, controlled, or maintained. U.S. Pat. No. 7,975,960 to Cox et al and U.S. Pat. No. 8,220,740 to Cox et al, owned in common with the present application, describe a nose wheel control apparatus capable of driving a taxiing aircraft without the use of the aircraft main engines or tow vehicles. Controlling and/or maintaining a set aircraft ground travel speed or a direction of travel is not described, however.
Automotive cruise control systems are well known and widely available for setting, controlling, and maintaining a set vehicle travel speed. However, like aircraft autopilot flight speed control systems, speed is controlled by adjusting engine throttle settings in available automotive speed control systems. Although speed control in electric automobiles has been suggested theoretically, there are significant differences and design considerations to be overcome in adapting a theoretical automotive system to drive an aircraft on the ground at a set, maintained taxi speed. Automotive cruise and speed control systems, moreover, do not automatically control direction of travel.
A need exists, therefore, for a system and method for setting a desired aircraft ground speed or direction of travel and automatically maintaining a set ground travel speed or direction for an aircraft equipped with a drive means that powers one or more aircraft wheels to move the aircraft during ground travel without the use of aircraft engines. Such a system and method would overcome the deficiencies of the prior art and permit efficient autonomous aircraft ground travel, leaving a pilot free to focus on taxi tasks other than controlling and/or maintaining the taxi speed required to produce optimum taxi procedures and effective airport surface traffic management.